The metric where not only the desired channel is
estimated, but also the interfering channel as well is given below. Note for this case, hypothesis signals
for both the desired and interfering signals are required.
(6.91)
One last comment to make here is that we have assumed symbol-sampled data in the metric. This
can be extended to using fractionally spaced MLE processing which can have additional benefits. In this
case, the metrics are computed for each of the timing phase instances of the over-sampled signal and
then the respective metrics are calculated and then combined across antennas and timing instances.
6.3 FREQUENCY DOMAIN EQUALIZATION
In this next section, we will provide an overview of frequency domain equalization (FDE) applied to
single carrier (SC) systems [21]. We have presented the time-domain equalization methods since they
are effective in combating ISI and suppressing interference. Some of the motivation in moving our attention
to the frequency domain are that OFDMA-based systems are proposed for the next generation of
wireless communications, hence requiring frequency domain signal processing. Also as the user data
rate increases the complexity of the equalizer grows since more symbols now span across the same channel
delay spread.
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